Wire bonding is a commonly used interconnection technology in the microelectronics manufacturing and packaging industry. More specifically, a wire bonder (also known as a wire bonding machine) forms wire interconnections between respective locations to be electrically interconnected, such as to connect a bond pad of a semiconductor device to a lead frame or carrier. Wire bonding machines be used to form conductive bumps (which bumps may, or may not, be used in connection with wire loops).
The ultrasonic system of a wire bonder comprises an ultrasonic generator and a transducer. The generator provides electrical power to the transducer at a given frequency. The transducer typically includes a driver such as a stack of piezoelectric elements (e.g., piezoelectric crystals, piezoelectric ceramics, etc.). Electrical energy is applied to the driver and the driver converts the electrical energy to mechanical energy. The mechanical energy is transferred to a bonding tool tip that oscillates with an amplitude corresponding to the applied electrical energy.
A conventional wire bonding process involves the following steps: (1) a wire is placed in contact with a bonding pad, and a bonding tool is placed on top of the wire; (2) the bonding tool applies pressure against the wire, forcing the wire against the bonding pad; (3) the ultrasonic generator applies a high frequency power signal to the transducer, which transduces the signal into an ultrasonic vibration, causing the bonding tool to oscillate in the plan of the bonding pad; (4) the friction between the wire and the bonding pad is overcome, and the wire scrubs against the surface of the bonding pad, causing localized softening and plastic flow of the wire and/or bonding pad; (5) after several milliseconds of scrubbing, the transducer is de-energized, which stops the motion of the bonding tool and wire and allows a weld to form between the wire and the bonding pad; and (6) the bonding tool is lifted away from the now bonded wire.
Certain factors may cause the bond to be defective. For example, a bond may not form properly if the bonding pad or the wire is not clean, the transducer may be energized too long (which may cause overheating of the materials or fracturing of the substrate), or there may be misalignment or curvature of the substrate. Curvature of the substrate, which may be due to warpage caused by thermal mismatch between the substrate layers, may cause a decrease in the oscillation amplitude of the bonding tool tip. An air gap that is created when the substrate is warped may cause the ultrasonic vibrations to be dispersed throughout the substrate and the air gap, which reduces the frictional force at the tip of the wire bonding tool, decreases pressure bonding strength and/or promotes improper bonding. As a result, the wire may peel away from the surface of the bond pad or the substrate. An improper or faulty electrical connection between the electrical components, such as semiconductor chips, integrated circuits (ICs), resistors, transistors, capacitors, and the like, and the substrate can lead to functional failure of the device or equipment which the faulty connection occurs.